An interior permanent magnet motor (hereinafter, referred to as an IPM motor as appropriate) in which permanent magnets are embedded in a rotor core is known as an electric motor for driving an electrically driven vehicle such as an electric vehicle or a hybrid vehicle.
The IPM motor has a problem that efficiency in a high rotation region is reduced by iron loss caused by magnetic fluxes of the permanent magnets. Further, it is required to reduce torque ripple to suppress vibration and noise of the electric motor.
Further, in terms of ensuring durability of an inverter component, it is also necessary to prevent a peak value of an induced voltage from exceeding a withstand voltage of an inverter system. The induced voltage is generated by synthesizing a main component contributing to torque and a harmonic component not contributing to torque. If the induced voltage is merely reduced so as not to exceed the withstand voltage of the inverter system, the main component may become smaller and the torque may be reduced. Accordingly, to prevent a torque reduction, the peak value of the induced voltage needs to be reduced by reducing only the harmonic component.
To meet these requirements, two permanent magnets to be embedded in a rotor are used for each pole, and a groove is formed on the outer periphery of the rotor in which these permanent magnets are arranged in a V shape open toward a rotor outer peripheral side so that a groove center lies in an electrical angle range of 40° to 53° in JP2004-328956A.